Birchenbach first reported the reaction of silver nitrate and iodine with cyclohexene to give nitro and iodo-nitro adducts, but was disregarded until many years later
Nitryl iodide reaction has been used in the nitration of sugars
Silver nitrate with iodine would lead to INO2 that can be cleaved heterolytically ( such as I+ NO2-) or homolytically (production of free radicals)
Information about the stereochemistry of the addition of INO2, was obtained by reaction silver nitrate and iodine with 2-cholestene in ether
NMR data shows that iodine has a very strong anisotropic effect (C-19 methyl signal was at 8.83 ppm)
Anisotropic effect increases from chlorine to bromine to iodine
The nitro group in adduct 1 occupied the 3a site, that suggested that pseudohalogen was reacting as INO2 but as NO2I.
This was further supported by the regiochemistry of the reaction of silver nitrate and iodine with styrene
t-butyethylene was treated with silver nitrate and iodine and gave compound 11
Furthermore HI was eliminated leading to compound 12, a vinyl nitro
Reduction of compound 12 with NaBH4 gave compound 13, a saturated nitro compound
Adduct 1 was refluxed with silver nitrate in alcohol only a small amount of the nitro alkene was made, but when 1 was refluxed in methanol and silver oxide, 3-nitro-2-cholestene was formed in 99% yield
To further prove that NO2I forms, the solids created from the reaction of the silver nitrate with iodine were removed before the addition of the alkene
When 2-cholestene was added, 1 was formed but in a very poor yield
Dinitrogen tetroxide was added slowly to a 2-cholestene and iodine solution in nonpolar solvents; the end result was compound 1
Trans stereochemistry was observed suggesting that a stable pyramidal radical is formed or that quenching with iodine is a lot faster than inversion of the radical formed.
It is suggested that the nitroalklyl radical denoted as 1a becomes trapped quickly and efficiently by iodine and is then converted to compound denoted as 1b that furthermore supports the formation of a product that is kinetically controlled and also not favored sterically.
NO2I was added to both cis and trans stilbene; the product was a diastereoisomeric mixture
After NO2I was added to excess cis- stilbene, NMR data showed that unreacted stilbene in the crude product was only the cis isomer.
This was strong evidence that the nitro radical formation was irreversible
NO2I when reacted with toluene and methyl benzoate did not lead to any nitration suggesting that NO2I is not a good source of nitrylium ions
The remainder of the article was the experimental section that described all the experimental procedures.
Summary of Journal Article
Title: Addition of Nitryl Iodide to Olefins
A. Hassner, J.E. Kropp, G.J. Kent, J. Org. Chem.,1969, 34, 2628- 2632
http://dx.doi.org/10.1021/jo01261a030